Process for the production of benzonitrile



Patented Feb. 6, 1951 PRQCESS FOR THE PRODUCTION OF BENZONITRILE FrankA. li'ilimitas, Pitman, and Herbert E. Rasmussen, Woodbury, N. 3.,assignors to Socony- Vacuum Oil Company, Incorporated, a corporation oiNew York No Drawing. Application October 1, 1949, Serial No. 119,216

(01. Edd-465') 2 Claims.

This invention relates, broadly, to a process for producing benzonitrileand is more particularly concerned with a catalytic process for theproduction of benzonitrile from toluene and ammonia.

In accordance with the process disclosed and claimed in U. S. Patent No.2,450,632, benzonitrile is produced by reacting toluene with ammonia, inthe vapor phase and at elevated temperatures, and in the presence of acatalytic material containing molybdenum oxide. In accordance with thisprocess, it is essential to use a catalyst containing molybdenum oxide.

It has now been discovered that in the process otherwise disclosed inthe aforementioned patent, it is possible to plotain commerciallyfeasible conversions per pass of benzonitrile, in the absence ofcatalysts containing molybdenum oxide. It has been found that the use ofair in conjunction with cracking catalysts of the silica-alumina type inthe reaction between toluene and ammonia produces benzonitrile. In Viewof the relatively low cost of the cracking catalysts, the commercialadvantages of such a process over the process utilizing a molybdenumoxide catalyst are manifest.

Accordingly, it is an object of the present invention to provide aprocess for the production of benzonitrile. An important object is toprovide a catalytic process for the production of benzonitrile which isinexpensive and commercially feasible. A specific object is to providecommercially feasible conversions per pass and ultimate yields ofbenzonitrile in a catalytic process which comprises reacting toluenewith ammonia, in the vapor phase, at elevated temperatures, and in thepresence of air and a cracking catalyst of the silica-alumina type.Other objects and advantages of the present invention will becomeapparent to those skilled in the art from the following description.

Broadly stated, the present invention provides a process for theproduction of benzonitrile, which comprises contacting toluene withammonia, in the vapor phase, at temperatures varying between about 875F. and the decomposition temperature of ammonia, in the presence of acracking catalyst of the silica-alumina type, and in the presence of airin amounts upwards of about per cent by weight, based on the weight ofthe toluene.

The ratio of ammonia to toluene in the charge may vary over a wide rangewith little effect on the ultimate yield of benzonitrile. In general,the reaction mixture may contain as little as 2 mol per cent or as muchas 98 mol per cent .of toluene. Ordinarily, however, it is preferred touse charges containing between about 20 mol per cent and about 90 molper cent of toluene.

In accordance with the present invention, air is added to the reactionzone directly, or it may be charged in admixture with one or both of thereactants. In practice, it is preferred to charge the air in admixturewith the reactants. Air in amounts as small as 15 per cent, based on theweight of the toluene, produces the results contemplated herein.Ordinarily, however, air in amounts varying between about 30 per centand about per cent, based on the weight of the toluene, produces themost satisfactory results. It is to be understood, however, that air maybe used in amounts greater than about 75 per cent of the weight of thetoluene, it being within the skill of one versed in the art to determinethe optimum amount of air to be used in any specific operation.

The catalysts operative to produce benzonitrile by reacting toluene withammonia, in the process of the present invention, are those described inU. S. Patent No. 2,384,946. These bead cracking catalysts are hard,homogeneous, porous and dried inorganic oxide gel particles containingsilica and alumina. They are prepared by initially forming a hydrosol ofinorganic oxide including silica and alumina. The hydrosol is thenintroduced, in the form of separate globules, into a fluid medium whichis substantially immiscible with water and which is kept at atemperature below the boiling point of the hydrosol, whereby theglobules assume a spheroidal shape. The globules are kept in this mediumfor a period of time suflicient to effect gelation. The resulting gelspheroids are then washed with water to remove water-soluble salts, aresubsequently base exchanged with a solution containing a cation capableof replacing alkali metals, and, finally, are dried. For the purpose ofthe present invention, the SiOzIAlzOs weight ratio in the finished beadsshould fall within the range varying between about 20:1 and about 6:1.

By way of a non-limiting example, in practice, the foregoing is effectedby initially mixing aqueous solutions of sodium silicate and of aluminumsulfate, in suitable proportions to produce the desired SiO2ZA1203weight ratio in the final product. The resulting hydrosol is thenintroduced through orifices into the top of an 8-foot column of gas oilmaintained at room temperature (68 F.). The globules of hydrosol fallthrough the oil and gel before passing into a layer of water locatedbeneath the oil. The gel spheroids are carried from the bottom of thecolumn by a stream of water and on removal from the water, are washedwith petroleum naphtha to remove oil from their surfaces. The spheroidsare then first washed with water and subsequently with an aqueoussolution of ammonium chloride to replace zeolitically-held sodium ionswith ammonium ions. The latter can be driven off as ammonia gas by heat.The spheroids are then dried slowly and uniformly at 180 F. untilshrinkage is substantially complete. Drying is then continued at agradually increasing temperature up to about 1050 F. at whichtemperature, the spheroids are maintained for about two hours.

In operation, the catalyst becomes fouled with carbonaceous materialwhich ultimately aifects the catalytic activity. Accordingly, when theefficiency of the catalyst declines to a point where further operationbecomes uneconomical or disadvantageous from a practical standpoint, thecatalyst may be regenerated, as is well known in the art, by subjectingthe same to a careful oxidation treatment, for example, by passing astream of air 'or air diluted with flue gases or steam over the same,under appropriate temperature conditions and for a suitable period oftime, such as the same period of time as the duration of the catalyticoperation. Preferably, the oxidation treatment is followed by a purgingtreatment, such as passing over the catalyst a stream of purge gas, forexample, steam, nitrogen, carbon dioxide, hydrocarbon gases, etc.

The reaction or contact time, i. e., the period of time during which aunit volume of the reactants is in contact with a unit volume ofcatalyst, may vary between a fraction of a second and several minutes.Thus, the contact time may be as low as 0.01 second and as high as 20minutes. It is preferred to use contact times varying between 0.1 secondand one minute, particularly, between 0.3 second and 30 seconds. It mustbe realized that at best these figures are estimates based on the numberof assumptions. For all practical purposes, as in catalytic processes ofthe type of the present invention, the more reliable data on contacttime is best expressed, as is well known in the art, in terms of liquidspace velocities, in the present instance, the volume of toluene pervolume of catalyst per hour. Accordingly,

it has been found that the space velocities may be varied considerablyand that velocities varying between about on -fourth and about four arequite satisfactory for the purposes contemplated herein.

In general, the temperatures to be used in the process of the presentinvention vary between about- 875 F. and the decomposition temperatureof ammonia (about 1250-1300 F.), and, preferably, between about 900 F.and about 1075 F. The preferred temperature to be used in any particularoperation will depend upon the type of catalyst employed. Generallyspeaking, the higher temperatures increases the conversion per pass, i

carried out at subatmospheric, atmospheric or superatmosphericpressures. Superatmospheric pressures are advantageous in that unreactedcharge materials condense more readily. Subatmospheric pressures appearto favor the reactions involved, since the reaction products have alarger volume than the reactants, and hence, it is evident'from the LeChatelier-Braun principle that the equilibrium favors nitrile formationmore at reduced pressures. However, such pressures reduce the throughputof the reactants and present increased difficulties in recyclingunreacted charge materials. Therefore, atmospheric or superatmosphericpressures are preferred.

The present process may be carried out by making use of any of thewell-known techniques for operating catalytic reactions in the vaporphase effectively. By way of illustration, toluene and ammonia may bevaporized separately in preheating zone. The vaporized reactants arethen introduced, in suitable proportions, together with suitableproportions of air, into a reaction zone containing a catalyst of thetype defined hereinbefore. The reaction zone may be a chamber of anysuitable type useful in contact-catalytic op-' erations; for example, acatalyst bed contained in a shell or a shell through which the catalystflows concurrently, or countercurrently, with the reactants. The vaporsof the reactants are maintained in contact with the catalyst at apredetermined elevated temperature and for a predetermined period oftime, both as set forth hereinbefore, and the resulting reaction mixtureis passed through a condensing zone into a receiving chamber. It will beunderstood that when the catalyst flows concurrently, orcountercurrently, with the reactants in'a reaction chamber, the catalystwill be thereafter suitably separated from the reaction mixture bydisengaging bafiles, etc. The reaction mixture will be, predominantly, amixture of benzonitrile, hydrogen, unchanged toluene, unchanged ammonia,and air. The benzonitrile and the unchanged toluene will be condensed inpassing through the condensing zone and will be retained in thereceiving chamber. Benzonitrile can be separated from the unchangedtoluene by any of the numerous and well-known separation procedures,such as fractional distillation. Similarly, the uncondensed hydrogen andunchanged ammonia can be separated from each other by absorbing ammoniain a suitable medium and then recovering it. The unchanged toluene andammonia can be recycled to the process, with or without the addition offresh toluene or ammonia, or both. g It will be apparent that theprocess may be operated as a batch or discontinuous process as by usinga catalyst-bed-type reaction chamher in which the catalytic andregeneration operations alternate. With a series of such reactionchambers, it will be seen that as the catalytic operation is takingplace in one or more of the reaction chambers, regeneration of thecatalyst will be taking place in one or more of the ants-fresh orrecycled-will flow continuously through a reaction chamber.

The following specific examples are for the purpose of illustrating themode of preparing benzonitrile in accordance with the process of thepresent invention, and for the purpose of demonstrating the advantagesthereof. It is to be clearly understood that the invention is not to belimited to the specific catalyst disclosed hereinafter, or to theconditions and manipulations set forth in the examples.

EXAMPLES 1 TO 3 The reaction system included a reactor containing 100parts by weight of bead catalyst; preheating zones; a condensing zone; areceiving chamber; and gas separators and scrubbers. The catalyst usedwas a conventional bead cracking catalyst, prepared by the method setforth hereinbefore and containing silica and alumina in a weight ratioof 8:1, respectively. In each of the runs, toluene and ammonia werepreheated sepf arately in the preheating zones. The reactants werecontinuously charged, in the vapor phase, into the reactor in anammonia-toluene mol ratio varying between about one and about 1.3, atsuch a rate that the liquid space velocity was about 2.0. During thisoperation, air, when used, was introduced into the toluene streampassing into the preheater. The reaction mixture passed from thereactor, through the condensing zone, into a receiving chamber. Theunchanged ammonia, light gases and hydrogen were sent to the gasseparators and scrubbers where they were continuously scrubbed withwater. The hydrogen and light gases were metered and vented. The ammoniawas discarded. The benzonitrile and unchanged toluene were separated bydistillation; the benzonitrile was drawn ofi and the toluene wasrecycled to the toluene preheater.

The pertinent data and the results of each run are tabulated in Table I.

It will be apparent from the foregoing that the present process providesan efiicient, inexpensive, and safe process for obtaining benzonitrile.The process is of considerable value in making commercially availablerelatively inexpensive benzonitrile which is useful, for example, as anintermediate in organic synthesis, resin manufacture, etc.

Although the present invention has been described with preferredembodiments, it is to be understood that modifications and variationsmay be resorted to without departing from the spirit and scope of thisinvention, as those skilled in the art will readily understand. Suchvariations and modifications are considered to be within the purview andscope of the appended claims.

What is claimed is:

1. The process for producing benzonitrile, which comprises contactingtoluene with ammonia, in the gaseous phase, at a temperature varyingbetween about 875 F. and about 1250 F., and in the presence of air inamounts of at least about 15 per cent based on the weight of saidtoluene and of a catalyst consisting essentially of hard, homogeneous,porous and dried inorganic oxide gel particles containing silica andalumina in a weight ratio varying between about :1 and about 6:1,respectively, said gel particles being formed by forming a hydrosol ofinorganic oxide including silica and alumina, introducing said hydrosolin the form of separate globules into a fluid medium which issubstantially immiscible with water and which is kept at a temperaturebelow the boiling point of the hydrosol, whereby the globules assume aspheroidal shape, maintaining said globules in said medium for a periodof time sufficient to effect gelation to produce gel. spheroids, washingsaid gel spheroids with water to remove water-soluble salts, baseexchanging said gel spheroids with a solution containing a cationcapable of replacing alkali metals, and drying the washed and baseexchanged spheroids.

2. The process for producing benzonitrile,

i which comprises contacting toluene with armmonia, in the gaseousphase, at a temperature varying between about 900 F. and about 1075 F.,

and in the presence of air in amounts varying between about 30 per centand about per cent based on the weight of said toluene and of a catalystconsisting essentially of hard, homogeneous, porous and dried inorganicoxide gel particles containing silica and alumina in a weight ratiovarying between about 20:1 and about 6:1, respectively, said gelparticles being formed by forming a hydrosol of inorganic oxideincluding silica and alumina, introducing said hydrosol in the form ofseparate globules into a fluid medium which is substantially immisciblewith water and which is kept at a temperature below the boiling point ofthe hydrosol, whereby the globules assume a spheroidal shape,maintaining said globules in said medium for a period of time sufficientto efiect gelation to produce gel spheroids, washing said gel spheroidswith water to remove water-soluble salts, base exchanging said gelspheroids with a solution containing a cation capable of replacingalkali metals, and drying the washed and base exchanged spheroids.

The following references are of record in the file 01 this patent:

UNITED STATES PATENTS Name Date Cosby et a1 Feb. 28,. 1950 OTHERREFERENCES Berkman et al.: Catalysis (Reinhold) pp. 782, 801, 803, 804(194.0).

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1. THE PROCESS FOR PRODUCING BENZONITRILE, WHICH COMPRISES CONTACTINGTOLUENE WITH AMMONIA, IN THE GASEOUS PHASE, AT A TEMPERATURE VARYINGBETWEEN ABOUT 875* F. AND ABOUT 1250* F., AND IN THE PRESENCE OF AIR INAMOUNTS OF AT LEAST ABOUT 15 PER CENT BASED ON THE WEIGHT OF SAIDTOLUENE AND OF A CATALYST CONSISTING ESSENTIALLY OF HARD, HOMOGENEOUS,POROUS AND DRIED INORGANIC OXIDE GEL PATICLES CONTAINING SILICA ANDALUMINA IN A WEIGHT RATIO VARYING BETWEEN ABOUT 20:1 AND ABOUT 6:1,RESPECTIVELY, SAID GEL PARTICLES BEING FORMED BY FORMING A HYDROSOL OFINORGANIC OXIDE INCLUDING SILICA AND ALUMINA, INTRODUCING SAID HYDROSOLIN THE FORM OF SEPARATE GLOBULES INTO A FLUID MEDIUM WHICH ISSUBSTANTIALLY IMMISCIBLE WITH WATER AND WHICH IS KEPT AT A TEMPERATUREBELOW THE BOILING POINT OF THE HYDROSOL, WHEREBY THE GLOBULES ASSUME ASPHEROIDAL SHAPE, MAINTAINING SAID GLOBULES IN SAID MEDIUM FOR A PERIODOF TIME SUFFICIENT TO EFFECT GELATION TO PRODUCE GEL SPHEROIDS, WASHINGSAID GEL SPHEROIDS WITH WATER TO REMOVE WATER-SOLUBLE SALTS, BASEEXCHANGING SAID GEL SPHEROIDS WITH A SOLUTION CONTAINING A CATIONCAPABLE OF REPLACING ALKALI METALS, AND DRYING THE WASHED AND BASEEXCHANGED SPHEROIDS.